1. Volume 123, Issue 5, Pages 861-873 (December 2005)
GroEL1: A Dedicated Chaperone Involved in Mycolic Acid Biosynthesis during Biofilm Formation in Mycobacteria 
Anil Ojha, Mridula Anand, Apoorva Bhatt, Laurent Kremer, William R. Jacobs, Graham F. Hatfull 
Cell 
Volume 123, Issue 5, Pages (December 2005)
DOI: /j.cell
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2. Figure 1 M. smegmatis groEL1 Encodes an Unusual Hsp60 Chaperone
(A) Organization of the groES, groEL1, and groEL2 genes in M. smegmatis (upper panel) and M. tuberculosis H37Rv (lower panel). groEL1 is cotranscribed with groES, while groEL2 is located more than 750 kbp away in both genomes; chromosomal locations (in italic type) are shown in kb. Phage Bxb1 integrates into the attB site in groEL1 as shown.
(B) Mycobacterial GroEL1 proteins and their counterparts in other actinomycetes contain a histidine-rich C terminus (shown in red); GroEL1 proteins of M. smegmatis (Ms), M. tuberculosis (Mtb), Nocardia farcinica (Nfa), Streptomyces albus (Sab), and Corynebacterium glutamicum (Cgl) are shown, as are the GroEL2 proteins of M. smegmatis and M. tuberculosis, which contain glycine-methionine-rich C-terminal tails common to most GroEL proteins. Integration of either phage Bxb1 or the integration vector, pAIK6, generates a different C terminus (shown in green), and integration by plasmid pAIKstop makes a truncated protein.
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3. Figure 2 GroEL1 Is Required for Biofilm Formation
(A) Bxb1 lysogens are defective in biofilm formation. M. smegmatis mc2155 (I) and lysogens of phages L5 (II), Bxb1 (III), and Che12 (IV) were grown on a liquid surface at 30°C for 7 days; insets show 4×-magnified portions of the biofilm.
(B) Interruption of the M. smegmatis groEL1 gene by integration of the Bxb1 integration-proficient plasmid vector, pAIK6 (I), integration of the plasmid pAIKstop, which terminates 18 residues from the C terminus of GroEL1 (II), or by deletion (III) results in loss of biofilm formation; complementation with wild-type groEL1 restores biofilm formation (IV).
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4. Figure 3
M. smegmatis GroEL1 Is Required for Biofilm Maturation but Not for Attachment
(A) Time course of biofilm development at a liquid-air surface. Dishes containing liquid growth medium were inoculated with either M. smegmatis mc2155 or a ΔgroEL1 mutant, and biofilms were allowed to develop for 7 days at 30°C. At day 3, M. smegmatis mc2155 forms a thin film across the surface of the medium, and by day 4 it begins to form a textured mature biofilm that continues to develop until day 7. The ΔgroEL1 mutant forms a similar film to the parent strain mc2155 by day 3 but does not develop further.
(B and C) Attachment of M. smegmatis mc2155 and ΔgroEL1 mutant to a PVC surface. Strains were transformed with a GFP-expressing plasmid, grown on PVC slides for 7 days, and viewed by fluorescence microscopy. The ΔgroEL1 cells attach as a monolayer to the PVC but do not form a mature biofilm, as further illustrated in the Z sections derived from confocal microscopy of the 7-day slides as shown in (C); horizontal lines indicate the approximate position of the surface, and vertical arrows show the direction of biofilm growth away from the surface.
(D) Growth of M. smegmatis in biofilm dishes. Following inoculation of medium as described in (A), viable cell counts were determined at various times, showing that ΔgroEL1 growth is compromised after 3 days of incubation.
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5. Figure 4
GroEL1 Is Required for Mycolic Acid Biosynthesis during Biofilm Formation
(A) 2D-PAGE reveals two protein species present at reduced levels in the ΔgroEL1 mutant relative to its mc2155 parent in stationary phase cells; identities of the protein spots were determined by either N-terminal sequencing or mass spectometry.
(B) Western blot analysis of total KasA/KasB levels during logarithmic planktonically grown cells reveals similar levels in ΔgroEL1, mc2155 parent, and complemented strains. The antibody recognizes both KasA and KasB, which migrate similarly, as well as the slowly migrating 80 kDa complex (indicated by arrow) that also contains AcpM (Mdluli et al., 1998).
(C) Western blot analysis of KasA/KasB separated by 2D-PAGE shows a single KasB and two KasA protein species. The level of the more basic of the two KasA spots (shown by arrow) varies under different growth conditions, but all KasA/KasB species are reduced in the ΔgroEL1 mutant after 7 days of biofilm growth.
(D) The reduction of KasA and KasB in the ΔgroEL1 mutant begins at day 4, correlating with the cessation of growth and inability to transition to biofilm maturation.
(E) Thin-layer chromatography of radiolabeled fatty acid methyl esters (FAMEs) and mycolic acid methyl esters (MAMEs) shows that the biosynthesis of all mycolic acid subclasses (α, α′, and epoxy) is dramatically reduced in the ΔgroEL1 mutant during biofilm maturation but not in planktonic cultures.
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6. Figure 5 Physical Association of GroEL1 and KasA
(A) M. smegmatis GroEL1 binds to Nickel-affinity columns. Extracts of M. smegmatis mc2155 (lanes 1), ΔgroEL1 mutant (lanes 2), and a pAIK6stop recombinant were bound to an Ni-affinity column and proteins eluted with either 20 mM or 75 mM imidazole as indicated. The position of GroEL1 is indicated with an arrow.
(B) SDS-PAGE was used to separate either GroEL1 eluted from an Ni-affinity column (lanes 1), a total extract from M. smegmatis mc2155 (lanes 2), or an extract from a ΔgroEL1 mutant (lanes 3). Proteins were transferred to a membrane and blotted with either polyclonal antibodies raised against E. coli GroEL or monoclonal antibodies raised against GroEL2 of bacilli Calmette Guerin (BCG, as indicated). Coomassie blue–stained proteins are shown in upper panel. Both antibodies recognize a 60 kDa protein in the ΔgroEL1 strain, showing that they both recognize GroEL2. However, only the E. coli antibody recognizes the protein eluted from the Ni-column, showing both that the BCG-GroEL2 monoclonal antibody does not recognize GroEL1 and that the protein eluted from the Ni-column contains GroEL1 and not GroEL2.
(C) Interaction between GroEL1 and KasA in planktonic and biofilm cells. Extracts from planktonic (pl) or biofilm (bio) samples from M. smegmatis mc2155, ΔgroEL1, and Δsmeg4308 were passed over an Ni-affinity column, and the proteins were eluted with 75 mM imidazole and separated by SDS-PAGE. Lane 2 contains 2 μg of purified KasA protein. The upper panel shows Coomassie blue–stained proteins, whereas the lower panel shows a Western blot of the same samples (and 20 ng of purified KasA) using anti-KasA serum.
(D) A Δsmeg4308 mutant is defective in biofilm formation. Biofilms were grown as in Figure 3, and the Δsmeg4308 mutant shows a mild defect such that mature biofilm features are not seen at day 5 but begin to appear at day 7.
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7. Figure 6
The Ratio of Short- to Long-Chain Mycolates Increases during Biofilm Formation
(A, B, C, and D) Total mycolates were extracted from M. smegmatis mc2155 cells (A and B) or ΔgroEL1 (C and D), growing in either log-phase planktonic (A and C) or 4-day biofilm (B and D) conditions and analyzed by MALDI-TOF mass spectrometry. Short-chain fatty acids (C56–C68) are seen as a series of peaks with masses ranging from 857 to 961.
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8. Figure 7
M. smegmatis Mutants Altered in Mycolic Acid Biosynthesis Are Also Defective in Biofilm Formation
(A) An inhAts strain is defective in biofilm maturation at 33°C and forms only thin films reminiscent of the ΔgroEL1 mutant (Figure 2B); the mutant grows similarly to mc2155 in planktonic growth (Figure S1). The biofilm defect is also observed at 30°C, but with a milder phenotype, and at 37°C there is significant impairment of planktonic growth (data not shown).
(B) Overexpression of KasA retards biofilm maturation, and a strain carrying a plasmid overexpressing KasA from the hsp60 promoter (pMV261:kasA) is slower in biofilm maturation than a vector-containing strain (pMV261). Both strains grow at similar rates planktonically (Figure S1).
(C) MALDI-TOF mass spectrometry of mycolates from 4-day biofilm cultures of mc2155pMV261:KasA showing reduced levels of C56–C68 fatty acids.
Cell  , DOI: ( /j.cell )
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